1. Field of the Invention
This invention relates to pressure transducers, and more particularly to pressure transducers capable of withstanding high overload pressures.
2. Description of the Prior Art
A common problem often encountered in pressure measuring systems is that the transducer may from time to time be subjected to overloads which greatly exceed the pressure measuring range of the transducer. This problem is particularly prevalent in differential pressure measurement systems where the line pressure may be a factor of hundreds or thousands times the anticipated maximum differential pressure, and overloads often occur under startup conditions. The problem also exists in many gage and absolute pressure measurement applications, but the severity is commonly greatest in high line pressure, low differential pressure systems.
Protecting the transducer against such overloads, particularly in systems where the transducer has a very low volumetric displacement, has posed a difficult problem for many years. It has been known to use a liquid filled transducer which includes valving means to limit the displacement of the transducer sensing element so as to protect it. The valve closes a fluid passageway through the transducer under overload conditions so that further displacement is prevented. Such a system for protecting a transducer against overload is disclosed in U.S. Pat. No. 3,765,256 and also in U.S. Pat. No. 3,559,488. The transducers described in the aforementioned patents utilize an "O" as the sealing element of the valving means and accordingly require a substantial displacement to assure sealing.